This part of the lecture led us to discuss the very notion of the nervous system. This was done on the basis of light perception in unicellular organisms. We started from the idea of separating the light stimulus, which depends on photon-sensitive structures, from the analysis of this stimulus, which requires nerve centers.
We compared the structures of photon receptors in bacteria, unicellular eukaryotes and metazoans, thus introducing the question, still debated today, of the monophyletic or polyphyletic origin of the eye. We presented the opposing theories and, together with Walter Gehring, took a stand in favor of a monophyletic origin. This point was discussed again later in the lecture.
